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SunnyDays

ERA5 almanac — 8 years of real data

Bali in September

Bali in September: 70% of days see measurable rain, 77°F average high, 9% of days historically clear (n=240, ERA5 2018–2025).

Bali in September is historically a poor month for sun: only 9% of days clear across 8 years (n=240, avg high 77°F). May is the clearest month for Bali historically. Historical average, not a forecast.

What you are reading: 8-year historical averages from the ERA5 reanalysis, not a forecast. A month that is historically 90% clear can still be overcast on your specific trip. For this week’s actual forecast, see the live Bali page. Both can be true at once: “historically strong in this month; this particular week is not.” We label which is which.

Early vs. Late September

Clear-sky percentage for Bali in September, split by half-month. “n” is the number of days sampled across 8 years (2018–2025).
Period % Clear days Sample (n) Avg high
Early September
1st–15th		 8% n=120 77°F
Late September
16th–end		 10% n=120 77°F
Full month average 9% n=240 77°F

Sunshine & warmth in September

A second measure using actual sunshine hours (ERA5 sunshine_duration), not the daily weather code. A Lowcountry day with 12 hours of sun and a 25-minute afternoon storm is counted below as a warm, sunny day — because it was. How we define this.

Sunshine-based metrics for Bali in September. Primary: % of days ≥ 72°F with > 6 h of sunshine.
Period Warm & sunny (≥72°F, >6 h sun) Sample (n)
Early September
1st–15th		 96% n=120
Late September
16th–end		 98% n=120
Full month average 97% n=240
11.2 h median sunshine per day 93% of days exceed 8 h sunshine 70% of days see ≥ 1 mm rain — rain is not hidden
Comparison (old vs new): WMO-code “clear” bar: 9%. Sunshine-based “warm & sunny”: 97%. The 88-point gap is from brief afternoon convective storms that stamp the whole day as “rain” in the WMO code but leave the bulk of the sunshine untouched.

Bottom line

Bali is a poor choice for sun in September: just 9% of days clear historically (n=240). May is the historically strongest month for sun here. The 8-year record is consistent — this is not a fluke bad stretch.

→ See all destinations in May — historically the best month for sun in Bali.

Every month in Bali

Compare across all months with data. Numbers are historical clear-sky %.

Historical clear-sky % for Bali, all months, ERA5 2018–2025.
Month % Clear Sample (n)
January 3% n=248 All destinations →
February 1% n=226 All destinations →
March 0% n=248 All destinations →
April 8% n=240 All destinations →
May 10% n=248 All destinations →
June 6% n=240 All destinations →
July 5% n=248 All destinations →
August 10% n=248 All destinations →
September ← this page 9% n=240 All destinations →
October 8% n=248 All destinations →
November 2% n=240 All destinations →
December 2% n=248 All destinations →

Frequently asked

Does it rain in Bali in September?

Yes, frequently. In Bali, 70% of days in September see measurable rain, based on 8 years of ERA5 historical data (n=240 days, 2018–2025). This is a historical average, not a forecast.

Is Bali good for sun in September?

Not usually. Bali is historically overcast in September: only 9% of days are clear (avg high 77°F, n=240 days, ERA5 2018–2025). May is historically far better for sun here.

All percentages are historical averages from the ERA5 reanalysis via Open-Meteo, 8 full years (2018–2025). “Clear” means avg high ≥ 72 °F, precipitation < 1 mm, and a non-precipitation weather code. This is history, not a forecast. The live 7-day outlook for any destination is on its own page and may differ from the long-run average. Data from Open-Meteo.